1. Technical Field of the Invention
The present invention relates generally to a rotor temperature control system for use in centrifuges. More particularly, the invention relates to a rotor temperature control system which is operable to modify an operation factor of a temperature regulating device based on an ambient temperature to control the temperature of a rotor in which samples to be separated are disposed to a target rotor temperature.
2. Background Art
There is known an ON-OFF rotor temperature control system utilizing an instant temperature value of a rotor of a centrifuge. This temperature control system, as shown in FIG. 8, modifies an operation factor of a temperature regulating device to 100% when the temperature of the rotor is higher than a target level by an error E, while when the rotor temperature is lower than the target level, the operation factor is set to 0%.
This conventional system, however, raises a drawback in that due to a control time lag occurring between temperature detection of the rotor and temperature regulation of the rotor, a ripple of the rotor temperature, as shown in FIG. 9, becomes relatively great under the control.
For avoiding the above problem, a proportional control (P control), as shown in FIG. 10, has been proposed in the art which changes an operation factor of a temperature regulating device in proportion to an error E developing between an actual rotor temperature and a target rotor temperature. However, the proportional control also suffers from the following drawback. The moment the error E is reduced to zero, the operation factor is also set to zero. With the lapse of time, however, the rotor temperature rises above the target rotor temperature to produce a small error again since the target rotor temperature is usually set to a value lower than ambient temperatures and the temperature regulating device is warmed by the ambient air. Upon development of this error, the operation factor is increased again (e.g., several percentages D), however, the activities of elevating the rotor temperature and restricting same are balanced with each other, ultimately producing an error e.
For eliminating the error e, the so-called PI control using integral action (I action) along with the P control is known. The integral action is such that the error e is added in time-sequence to derive a correction value to correct the operation factor based thereon. As shown in FIG. 12, according to the PI control, an operation factor D corrected based on an integration value of the error e is provided to regulate the temperature of the rotor to a target rotor temperature.
The above PI control, however, gives rise to a problem in that a response rate relative to variation in rotor temperature becomes low due to the time-sequential integration of the error e produced. In order to improve this response rate, the technique, referred to as PID control, using differential control (D control) in addition to the PI control has been proposed in the art. In this differential control, the operation factor is further corrected based a variation (differential value) in rotor temperature.
In the above discussed conventional rotor temperature control systems, the operation factor of the temperature regulating device is changed in proportion to the error E between the actual rotor temperature and the target rotor temperature. Thus, in the case where at the start of operation of a centrifugal unit, a great temperature difference, or error is developed between the rotor temperature and the target rotor temperature, the operation factor of the temperature regulating device is set to a greater value so that the rotor temperature reaches the target rotor temperature quickly. However, when the rotor temperature initially falls in a range in the vicinity of the target rotor temperature so that the error E is small, the operation factor of the temperature regulating device is set to a smaller value, undesirably requiring relatively long period of time for the rotor temperature to reach the target rotor temperature. In other words, a drawback in encountered in that the operation factor of the temperature regulating device is greatly dependent upon the degree of the temperature error between the rotor temperature and the target rotor temperature.
Additionally, in common use of centrifuges, for accurate separation in a short period of time or preventing samples in a rotor from being damaged, it is often the case that the rotor is initially cooled to a temperature close to a target rotor temperature prior to separation operation. In this case, likewise to the above, a great deal of time is required for the rotor to reach the target rotor temperature.